The past few years have seen some serious discussion among conservation biologists about the biodiversity value of invaded communities. For example, to what degree do some invasive species integrate into native communities, how extensive and permanent are the damages from invasives, and are native species able to evolve in response? It is important to resolve these questions regarding the ecology of invasives, in order to inform policy and management questions, such as: is it worth struggling to keep native communities pristine against the rising tide of invasions? What is the implication of decelerating rates of invasion over time due to adaptation by natives, or switch by some native herbivores to browsing on the invasive?
An interesting question among this discussion about invaded communities concerns the puzzling observation that some rare plants still persist in areas heavily invaded by a non-native plant. While invasive plants can and do drastically alter the physical landscape (e.g. honeysuckle, kudzu), they rarely lead (on their own) to complete extinction of native plants. Why might this be?
A new study in the journal Science sheds some light on why rare plants are able to persist. By studying highly invaded and relatively uninvaded plots of different sizes in three very different communities (Hawaii, Florida, and Missouri), Kristin Powell and colleagues found that invasive species do eliminate many species in local areas (several meters) but that across much broader areas (hundreds of meters), species abundance is hardly affected. Invasive species clearly have strong effects, there is no doubt about that, but over broad scales native species find a refuge somehow. One reason that native rare plants may be less affected by invasive plants than more common native plants is that rare plants may have a particular microhabitat to exploit, or they may perform well in the heavily shaded areas that are invaded. You can read more here, and here.
The study emphasizes that when we discuss the effects of invasive species, we should discuss local, regional, and global scale effects, as the outcome for biodiversity is different on these levels. We should also be aware that invasive species will affect different taxa in different ways. In the end, the study offers some hope that invaded ecosystems retain the capacity to recover with some management assistance, as most of the native species are still there, holding on.